JPS6251898B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing yellow iron oxide. More specifically, the present invention relates to a method for producing yellow iron oxide suitable as a raw material for producing magnetic iron oxide powder. Generally, yellow iron oxide (α-FeOOH) is reduced,
Or, after this reduction, the particle shape of the magnetic iron oxide produced by oxidation depends on the yellow iron oxide that is the starting material. Therefore, in order to obtain high-grade magnetic iron oxide, the properties of yellow iron oxide are extremely important. In recent years, with the development and higher performance of magnetic recording equipment, magnetic iron oxide is also required to have higher performance. In general, to improve the magnetic properties of magnetic iron oxide,
The particles must be uniform in particle size and have a large axial ratio (major axis/width). The size of the particles is also important. In other words, the finer the particle size and the larger the axial ratio, the
Although the magnetic properties of magnetic iron oxide powder are improved,
Since its dispersibility tends to deteriorate, when used in recording materials such as magnetic tapes, it not only fails to take advantage of its original properties, but also leads to an increase in dispersion costs. As mentioned above, since the particle shape of magnetic iron oxide depends on the yellow iron oxide, yellow iron oxide with a uniform particle size and a large axial ratio is required. Conventionally, as a method for producing yellow iron oxide, there is a method in which an alkali is added to a ferrous salt solution to form a ferrous hydroxide precipitate, and the precipitate is air-oxidized. At least, this method yields needle-shaped yellow iron oxide crystals, but the yellow iron oxide crystals grow around hardly soluble ferrous hydroxide crystals (hexagonal plate shape), and the needle-shaped particles interact with each other. This method tends to result in a branched agglomerated structure.
It is a reaction to obtain hardly soluble yellow iron oxide from iron oxide, and it is extremely difficult to adjust the particle size of the product and make it uniform by adjusting the manufacturing conditions. In recent years, a method has been proposed to obtain yellow iron oxide by heating and aging ferric hydroxide, but this method tends to produce granular α-Fe ₂ O ₃ as a by-product _; O ₃ has a negative effect on the crystal growth of yellow iron oxide, making it impossible to obtain uniform grain size. As described above, in any of the methods, yellow iron oxide with uniform particle size and large axial ratio cannot be obtained. As a method for adjusting the particle size of yellow iron oxide, there is a method in which yellow iron oxide is subjected to pressure hydrothermal treatment in water or an alkali of 10N or less (Japanese Patent Publication No. 53-28158, Method for Improving Characteristics of Yellow Iron Oxide Pigment). This method converts the fine imperfect crystals contained in yellow iron oxide into perfect crystals, makes the grain size uniform, and further improves the dimensional ratio of the needle-like crystals (reduces the axial ratio). When this method is applied to yellow iron oxide for magnetic materials, the major axis of the particles becomes smaller and the width (minor axis) increases, so the axial ratio decreases, the particle size is uniform, and the anisotropic magnetic field distribution is excellent. Although yellow iron oxide, which is a raw material for magnetic materials with good dispersibility, can be obtained, it is still desired to improve its performance. In view of the above circumstances, the inventors of the present invention have conducted extensive research in search of a method that takes advantage of the excellent properties of hydrothermal treatment, namely perfecting the crystals and making the grain size uniform, without reducing the axial ratio. The present invention was completed based on the finding that when acicular yellow iron oxide is subjected to hydrothermal treatment, the acicular crystals grow significantly in the major axis direction, resulting in yellow iron oxide with a large axial ratio and uniform particle size. This is what I did. That is, in the present invention, fine needle-shaped yellow iron oxide with a major axis of 0.4μ or less and a width of 0.04μ or less is mixed with water or
Dispersed in alkaline aqueous solution of 10N or less, 100 to 250℃
The long axis is 0.3 to 1.0μ and the width is 0.1.
The present invention provides a method for producing yellow iron oxide, which is characterized by obtaining crystals with a uniform particle size distribution consisting of single particles of μ or less in size. In the present invention, yellow iron oxide can be used regardless of its manufacturing method. The shape and size of the yellow iron oxide used are extremely important. That is, the finer and acicular the grain, the more remarkable the growth in the long axis direction, and the more uniform the grain size with a large axial ratio can be obtained. Moreover, the more extremely fine imperfect crystals are included, the greater the effect is. This growth in the major axis direction was discovered for the first time in the present invention. Therefore, the present invention is applied to fine yellow iron oxide having a major axis of 0.4μ or less and a width of 0.04μ or less, preferably a major axis of 0.3μ or less and a width of 0.03μ or less. As mentioned above, yellow iron oxide can be applied regardless of its manufacturing method, but it is particularly advantageous to apply it to fine branched yellow iron oxide obtained by oxidation of ferrous hydroxide. This is because, according to the present invention, particles with uniform particle size and no branching can be obtained. Further, an alkaline solution of yellow iron oxide obtained by air oxidation of ferrous hydroxide with an alkaline pH of 11 or above can be directly subjected to hydrothermal treatment. In this case, there is no need for separation operations, and it is economical. The medium for hydrothermal treatment is water or an alkaline aqueous solution of 10N or less. Alkali include sodium hydroxide, calcium hydroxide, sodium carbonate, potassium hydroxide,
Ammonia water etc. are used. The concentration of these is preferably 10N or less. At concentrations higher than this, α-Fe ₂ O ₃ alkali ferrite is produced. Furthermore, since the higher the alkali concentration, the larger the growth in the short axis (width) direction tends to be, it is preferable to carry out the process in an aqueous alkaline solution of 2N or less. Hydrothermal treatment temperature is 100℃~250℃, preferably
The temperature is between 150°C and 220°C. This is because at temperatures above 250°C, α-Fe ₂ O ₃ and alkali ferrite are produced, and below 100°C, crystal growth does not proceed. The hydrothermal treatment time varies depending on the treatment temperature, the size of the yellow iron oxide particles used, etc., but is usually from several minutes to several hours. When hydrothermal treatment is performed under the above conditions, the major diameter is 0.4μ.
In the following, the fine and irregular raw material yellow iron oxide with a width of 0.04 μm or less becomes a well-ordered yellow iron oxide with a major axis of 0.3 to 1.0 μm and a width of 0.1 μm or less. The yellow iron oxide obtained by this method can be reduced or
When reduced and then oxidized to produce a magnetic material, the particle shape changes very little, the particle size is uniform, the axial ratio is large, and the magnetic material has excellent magnetic properties. Furthermore, when sodium silicate or the like is added during hydrothermal treatment, yellow iron oxide with less change in particle shape can be obtained during reduction or oxidation treatment. The appropriate amount of sodium silicate added is 0.1 to 5.0% by weight based on yellow iron oxide. Furthermore, the magnetic material obtained from the yellow iron oxide obtained by the present invention has a long axis.
Since it is made up of single particles of 0.3 to 1.0μ and does not contain any fine particles, it has extremely good dispersibility. The present invention will be explained below with reference to Examples. In Examples and Reference Examples, all parts and % indicate weight, parts and weight %. Example 1 Yellow iron oxide (with a major axis of about 0.1 to 0.3μ and a width of about 0.01 to 0.03μ) obtained by adding caustic soda to an aqueous ferrous sulfate solution and air-oxidizing the produced ferrous hydroxide ( 40 parts of the electron micrograph (20,000 magnification shown in Figure 1) and 400 parts of 0.5N aqueous sodium hydroxide solution were placed in a Teflon-lined autoclave and heated to 200°C for 2 hours. After cooling, it was washed with water and dried. Figure 2 shows an electron micrograph of the yellow iron oxide obtained in this example at a magnification of 20,000. As is clear from FIG. 2, the yellow iron oxide of this example is a particle with a major axis of about 0.5 to 0.7 μ and a width of 0.04 to 0.06 μ, and grows in the major axis direction, and the axial ratio becomes large. The yellow iron oxide of this example was heated at 330°C in a hydrogen gas stream.
When heated for 1 hour and then air oxidized at 200° C. for 30 minutes to obtain γ-Fe ₂ O ₃ , the magnetic properties were extremely superior to that of the raw material yellow iron oxide of this example. The results are shown in Table-1.

[Table] Furthermore, when both were used as a paint for magnetic tape, the product of this example had excellent dispersibility when made into a paint. Furthermore, when made into a magnetic tape, the product of this example had excellent magnetic field orientation, high packing density, and good sensitivity. Reference Example 1 Hydrothermal treatment was performed under the same conditions as in Example 1 using a commercially available yellow iron oxide with a major axis of 0.5 to 1μ (electron micrograph, magnification 20,000 is shown in Figure 3). As a result, fine particles were reduced. However, a yellow iron oxide with a needle-like shape and a larger width was obtained. An electron micrograph of this yellow iron oxide is shown in Figure 4 (20,000 magnification). As is clear from this photograph, no growth was observed in the long axis direction. Example 2 Add 100 parts of ferrous sulfate aqueous salt (FeSO ₄ −7H ₂ O) to water.
Add 100 parts of sodium hydroxide to a solution of 1000 parts of sodium hydroxide.
A solution prepared by dissolving 500 parts of water was added thereto, and air oxidation was performed at 50°C to obtain an alkaline water slurry of yellow iron oxide. (This reaction solution always had a pH of 13 or higher.) This slurry was placed in an autoclave and heated to
After hydrothermal treatment at ℃ for 1 hour, the major diameter was 0.3 to 0.5μ.
Yellow iron oxide with a uniform particle size with a width of 0.02 to 0.04μ was obtained. Example 3 40 parts of yellow iron oxide used in Example 1, 400 parts of 1N sodium hydroxide aqueous solution, and sodium silicate
4 parts of Na ₂ SiO ₃ ) were heated at 200°C in an autoclave.
When heated for an hour, the major diameter of the silicic acid-covered material was 0.3
A yellow iron oxide of ~0.5μ and a width of 0.02-0.03μ was obtained. This product was converted into γFe ₂ O ₃ by the method described in Example 1.
As a result, the shape and size of the particles were almost the same as the original yellow iron oxide, and they had excellent magnetic properties and dispersibility. Example 4 Even when sodium hydroxide was used in place of the sodium hydroxide in Example 1, an excellent yellow iron oxide similar to that in Example 1 was obtained.

[Brief explanation of the drawing]

Each drawing is an electron micrograph (magnification;
20000). Figure-1; Raw yellow iron oxide used in Example 1; Figure-2; Yellow iron oxide obtained in Example 1; Figure-3; Commercially available yellow iron oxide used in Reference Example 1; Figure-4; Reference. Yellow iron oxide obtained in Example 1.

Claims (1)

[Claims] 1. The major axis is 0.4μ or less, and the width (minor axis) is 0.04
Fine needle-like yellow iron oxide (α-
FeOOH) is dispersed in water or an alkaline aqueous solution of 10N or less, heat-treated at 100-250℃, and the major axis is 0.3-
A method for producing yellow iron oxide, characterized by obtaining crystals having a single particle shape of 1.0μ and a width of 0.1μ or less. 2. The method for producing yellow iron oxide according to claim 1, which uses fine acicular yellow iron oxide obtained by air oxidation of ferrous hydroxide. 3. Claim 2 uses branched yellow iron oxide obtained by air oxidation of ferrous hydroxide.
The method for producing yellow iron oxide described in Section 1. 4. The method for producing yellow iron oxide according to any one of claims 1 to 3, using fine acicular yellow iron oxide having a major axis of 0.3μ or less and a width of 0.03μ or less. 5. The method for producing yellow iron oxide according to any one of claims 1 to 4, wherein the heat treatment temperature is 150 to 220°C. 6. The method for producing yellow iron oxide according to any one of claims 1 to 5, using an alkaline aqueous solution of 2N or less. 7 A dispersion solution of ferrous hydroxide is oxidized in air at pH 11 or higher, and the major axis is 0.4 μ or less and the width is
Heat-treating an alkaline aqueous dispersion of yellow iron oxide with a fine needle shape of 0.04μ or less at 100 to 250℃ to obtain crystals having a single particle shape with a major axis of 0.3 to 1.0μ and a width of 0.1μ or less. A method for producing yellow iron oxide characterized by: 8 Fine acicular yellow iron oxide with a major axis of 0.4μ or less and a width of 0.04μ or less is dispersed in water or an alkaline aqueous solution of 10N or less in the presence of sodium silicate.
A method for producing yellow iron oxide, which comprises performing heat treatment at ~250°C to obtain crystals having a single particle shape with a major axis of 0.3 to 1.0μ and a width of 0.1μ or less.